Precise positioning is of interest for indoor areas as well as outdoor areas where global navigation satellite system (GNSS) signals do not exist or have bad quality. Positioning techniques are often based on the use of wireless communication techniques.
For indoor systems, especially for Ultra-wide-band (UWB) based systems, the well-known Two-Way-Ranging (TWR) approach is a common choice. A main advantage of this approach is that there is no need for a fine synchronization between the stations performing the TWR.
Basically, TWR is performed between different nodes, which are also referred to as stations, in particular a transceiver node of unknown position and anchor nodes of known position. The transceiver node is a mobile device in many ranging or positioning applications. However, that is not a requirement. For two-dimensional positioning, at least three anchor nodes with known positions are required. For three-dimensional positioning, at least four anchor nodes with known positions are required. If more than the required minimum number of anchor nodes are present, the precision of positioning can be additionally improved. The number of anchor nodes can be reduced if additional constraints are introduced. Such constraints include known limitations of where the transceiver nodes can be.
However, TWR based methods do not cope well with a large number of mobile stations. Each mobile station has to perform TWR with the anchor nodes in order to estimate its position. For each TWR process, at least two transmissions are needed. In a multiuser scenario, where a lot of wireless mobile stations are present, an overall large number of transmissions are performed for positioning purposes. In a network which is also used for data communication, the transmissions needed for positioning thus introduce additional overhead in terms of channel usage. Depending on the number of users and the number of updates each user needs, the overhead can be substantial. This may require that the number of users allowed to make use of the positioning functionality is limited.